The present invention relates to a reinforced cell structure for confinement of material. Specifically, the present invention relates to a cell web material which has apertures that increase the load bearing capacity by improving the interface frictional angle.
Cellular confinement structures serve to increase the load bearing capacity, stability and erosion resistance of materials which are placed within the cells of the system. A commercially available system is Geoweb(copyright) plastic web soil confinement structure, sold by Presto Products, Incorporated, P.O. Box 2399, Appleton, Wis. 54913. Geoweb(copyright) cells are made from high density polyethylene strips which are joined by ultrasonic seams on their faces in a side by side relationship at alternating spacings so that when the strips are stretched out in a direction perpendicular to the faces of the strips, the resulting web section is honeycomb-like in appearance, with sinusoidal or undulant shaped cells. Geoweb(copyright) sections are light-weight and are shipped in their collapsed form for ease in handling and installation.
The web materials have been used extensively to provide road buses, subgrades or pavement systems. Structural foundations have been reinforced or stiffened with the web materials. Additionally, Geoweb(copyright) cells have been used to provide earth and liquid retention structures by stacking one web layer upon another, such as a stepped back design for hill slope retention. The Geoweb(copyright) cells also protect earth slopes, channels, revetments and hydraulic structures from surface erosion. Grass and other earth slope cover materials have been protected and stabilized through the use of the web cells Geoweb(copyright) cells can be infilled with various earth materials such as sand, rounded rock, granular soils and aggregates, topsoil, vegetative materials and the like. Concrete and soil-cement or asphaltic-cement can also be used to infill the cells.
Materials, such as stone, are ideal for construction because of their very high internal friction angles. The drawback with these construction materials are the lack of cohesion factors which result in the need to confine the materials. A cellular confinement structure, such as Geoweb(copyright), provides a cohesive factor by confining the materials, but does not provide the same friction angle because the confinement structure introduces a slip plane in which the stone has a lower interface friction angle. Therefore, the stone does not perform at its internal friction angle. If the interface friction angle can be increased, the load bearing capacity will also be increased.
An improvement in the load bearing capacity can result in stronger structural designs with higher factors of safety and more cost effective designs for civil engineering applications such as in road base or retaining wall designs. Load bearing capacity has been increased in a texturized cell material structure using a sand infill by the improvement of the interface friction angle. U.S. Pat. No. 4,965,097. However, the texturized cell wall does not perform as well in increasing the interface friction angle on larger construction materials, such as stone.
There is a need in the industry for a cell confinement structure that significantly improves load bearing capacity on construction materials, such as stone, by increasing the interface friction angle, while still maintaining the strength of the cellular confinement structure.
The present invention addresses the need to effectively provide an improved cellular web structure that increases the interface friction angle in construction materials such as stone. The result of improving the interface friction angle is an increase in the load bearing capacity of the cellular confinement structure.
Other important objectives obtained with this improved cellular web structure are as follows: a weight reduction of the cellular confinement structure which is especially useful on weaker subgrades; lateral drainage through the system which improves structure integrity; lock up of concrete infill and open areas for use with tendons reinforcements.
The present invention provides a cell structure for confinement of material having many elongated plastic strips in a side by side relationship that are bonded together in spaced-apart, limited areas in which the strips may be stretched in width to form a unitary web of cells. The strips form cell walls that have a plurality of apertures whose diameter can range between about 3 mm and about 17 mm.
In a preferred embodiment, each of the cell walls has many apertures. If aesthetics is a concern, a non-aperture cell wall can be bonded with open cell walls. The diameters of the apertures in the cell walls are approximately 10 mm with the area of the apertures comprising approximately 19 to 28% of the total area of the cell wall surface. The plurality of apertures increases the interface friction angle by approximately 5 degrees compared to a cellular confinement structure without a plurality of apertures. The apertures are aligned in staggered rows to maintain the hoop/column strength of the web structure.
In another embodiment, the cell walls have a plurality of apertures that are described in the preferred embodiment on a texturized surface. Additionally, a reinforcing means, such as a tendon, is used through the apertures. The addition of the reinforcing tendon is independent of the existence of the texturized surface.
Another aspect of the present invention is a method for preparing material to be used as cell walls in a cellular confinement structure that improves the cohesive factor and interface friction angle. The steps in this method are forming the plurality of apertures in the plastic strips of material and providing predetermined non-open areas of the plastic strips for securement to the other plastic strips. The above method is capable of being modified by adding a tendon by finding substantially coincident apertures among the plurality of apertures, guiding the tendon through these apertures, terminating the tendon at ends of the cell web and anchoring the tendon. The tendon is added after positioning the cell web.
While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof have been shown by example in the drawings and will herein be described in detail. It should be understood, however, that it is not intended to limit the invention to the particular forms disclosed, but on the contrary, the invention is to cover all modifications, equivalents and alternatives falling within the spirit and scope of the invention as defined by the appended claims.